Hill's lawyer, said he was relieved the stay had been issued just three hours before the execution was due to have taken place. Photograph: AFP/Getty Images

A judge in Fulton County, Georgia, has blocked the execution of Warren Hill, an intellectually disabled man who was set to be put to death by lethal injection despite a US supreme court ban on judicial killings of "mentally retarded" people.

Hill, 52, has been granted a slim window in which to argue that his rights have been violated by a recent state law that imposes secrecy on the drugs that would be used to kill him. Under the new Lethal Injection Secrecy Law, the identity of the suppliers of the sedative pentobarbital that would be given to him in a lethal dose has been deemed a "state secret" in an effort to bypass a growing international boycott of the use of pharmaceuticals in death sentences.

The Georgia state courts will now reconsider his case on Thursday. Should the judges decide that the execution can be put back on schedule, it is possible that by the end of this week Hill will be faced with his fourth brush with the death chamber in the space of a year.

Brian Kammer, Hill's lawyer, said he was relieved the stay had been issued just three hours before the execution was due to have taken place. "At this time, there is far too much we do not know about how the state intends to proceed in this, the most extreme act a government can take against a citizen," he said.

The decision to postpone the execution by just three days temporarily gets the US supreme court off the hook. Hill's legal team had appealed to the nine justices to intervene on the grounds that the same court prohibited executions for "mentally retarded" prisoners – as called in US jurisprudence – in 2002.

All nine medical experts who have examined Hill over the years are now in agreement that he is intellectually disabled. They include three doctors whose expert opinion in 2000 that the condemned man was not "retarded" was seminal in having him sent to his death – they now say that their initial view was rushed and based on outdated medical understanding.

The US supreme court will now be stood down in considering the Hill case while the lower state courts deliberate on the issue of the secrecy surrounding the lethal injection drugs. That flows from a legal challenge lodged last Friday that argues that the secrecy law leaves the prisoner "with no means for determing whether the drugs for his lethal injection are safe and will reliably perform their function, or if they are taineted, counterfeited, expired or compromised in some other way."

The legal challenge goes on to argue in the legal challenge that the uncertainty surrounding the drugs to be used to put him to death also constitutes another violation of the eighth amendment of the US constitution, rendering his pending execution this evening a singularly controversial event even by the standards of the US death penalty.